Frequency-translational bandpass filter with harmonic rejection
View Patent ↗A high quality factor frequency translated bandpass filter (FTBPF) with harmonic rejection includes multiple transconductance cells configured to convert a received radio frequency (RF) voltage signal into respective RF current signals. Each of the transconductance cells are weighted such that the FTBPF has an effective transconductance of a first magnitude for frequency components of the received RF voltage signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the received RF voltage signal arising from harmonics at integer multiples of the first harmonic. The FTBPF also includes multiple frequency conversion cells coupled to the transconductance cells and configured to mix respective ones of the RF current signals with multiple non-overlapping local oscillator signals. The FTBPF also includes multiple baseband impedances coupled to outputs of the frequency conversion cells and ground and are frequency translated by mixed signals from the frequency conversion cells.
1. A frequency translated filter, comprising:
a plurality of transconductance cells configured to convert a received radio frequency (RF) voltage signal into a respective plurality of RF current signals, wherein each of the plurality of transconductance cells provides an effective transconductance of a first magnitude for frequency components of the received RF voltage signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the received RF voltage signal arising from harmonics at integer multiples of the first harmonic;
a plurality of frequency conversion cells coupled to the plurality of transconductance cells and configured to mix respective ones of the plurality of RF current signals with a plurality of non-overlapping local oscillator (LO) signals; and
a plurality of baseband impedances coupled between outputs of the plurality of frequency conversion cells and ground, wherein the plurality of baseband impedances are frequency translated by mixed signals from the plurality of frequency conversion cells.
2. The frequency translated filter of claim 1 , wherein the plurality of transconductance cells and the plurality of frequency conversion cells employ single-ended inputs.
3. The frequency translated filter of claim 2 , wherein each of the plurality of transconductance cells is configured with a transconductance weighting equivalent to
k
[
1
+
cos
(
2
π
X
M
)
]
,
where X is an integer representing one of the plurality of transconductance cells, M is a number of LO signals employed, and k is an arbitrary constant that determines the effective transconductance of the transconductance cell.
4. The frequency translated filter of claim 1 , wherein the plurality of transconductance cells and the plurality of frequency conversion cells employ differential inputs.
5. The frequency translated filter of claim 4 , wherein each of the plurality of transconductance cells is configured with a transconductance weighting equivalent to
k
[
cos
(
2
π
X
M
)
]
,
where X is an integer representing one of the plurality of transconductance cells, M is a number of LO phases employed, and k is an arbitrary constant that determines the effective transconductance of the transconductance cell.
6. The frequency translated filter of claim 1 , wherein the plurality of non-overlapping LO signals have successive phase shifts substantially equal to 360/M degrees, where M is a number of the plurality of non-overlapping LO signals.
7. The frequency translated filter of claim 1 , wherein the plurality of non-overlapping LO signals each correspond to a fundamental frequency.
8. The frequency translated filter of claim 7 , wherein the plurality of transconductance cells each receive an input impedance equivalent to the plurality of baseband impedances translated in frequency by the fundamental frequency.
9. The frequency translated filter of claim 1 , wherein the plurality of non-overlapping LO signals have identical magnitudes and are phase-shifted from one another.
10. The frequency translated filter of claim 1 , wherein each of the plurality of transconductance cells produces a transconductance gain according to an output voltage equivalent to
V
OUT
=
∑
0
M
-
1
V
OUT
〈
X
〉
(
ⅇ
j2π
X
M
)
,
where j is an imaginary unit, where X is an integer representing one of the plurality of transconductance cells, and M is a number of the plurality of non-overlapping LO signals.
11. The frequency translated filter of claim 1 , wherein each of the plurality of transconductance cells is configured with a transconductance weighting that causes the effective transconductance of the frequency-translated filter to be non-zero when excited by a received RF voltage signal arising from a harmonic within a frequency band of interest but zero for a received RF voltage signal arising from harmonics outside the frequency band of interest.
12. The frequency translated filter of claim 1 , wherein each of the plurality of baseband impedances includes a capacitor.
13. A radio frequency (RF) receiver comprising:
a plurality of transconductance cells configured to configured to convert a received RF signal into a plurality of RF current signals proportional to a voltage corresponding to the received RF signal, wherein each of the plurality of transconductance cells has an effective transconductance of a first magnitude for frequency components of the received RF signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the received RF signal arising from harmonics at integer multiples of the first harmonic; and
a frequency translated bandpass filter coupled to the plurality of transconductance cells and configured to produce a filtered inbound RF signal.
14. The RF receiver of claim 13 , wherein the frequency translated bandpass filter comprises:
a plurality of frequency conversion cells coupled to the plurality of transconductance cells and configured to mix respective ones of the plurality of RF current signals with a plurality of non-overlapping local oscillator (LO) signals to produce respective mixed signals; and
a plurality of baseband impedances coupled to the plurality of frequency conversion cells and ground and configured to provide a high quality factor filter when frequency translated by the mixed signals.
15. The RF receiver of claim 13 , wherein each of the plurality of transconductance cells is configured with a transconductance weighting that causes the effective transconductance of the transconductance cell to increase up to the first magnitude when excited by the frequency components arising from the first harmonic and to decrease to the second magnitude for the frequency components arising from harmonics other than the first harmonic.
16. The RF receiver of claim 15 , wherein the transconductance weighting provides that wanted harmonics cause a current change through the transconductance cell.
17. The RF receiver of claim 13 , wherein the plurality of transconductance cells are configured to amplify frequency components of the RF signal arising from harmonics of a fundamental frequency.
18. The RF receiver of claim 17 , wherein the plurality of transconductance cells are further configured to amplify frequency components of the RF signal arising from more than one harmonic multiple of the fundamental frequency.
19. The RF receiver of claim 13 , wherein the frequency translated bandpass filter employs differential inputs.
20. The RF receiver of claim 19 , wherein each of the plurality of transconductance cells produces a transconductance gain according to an output voltage equivalent to
V
OUT
=
∑
0
M
2
-
1
V
OUT
〈
X
〉
(
ⅇ
j2π
X
M
)
,
where j is an imaginary unit, X is an integer representing one of the plurality of transconductance cells, and M is a number of LO signals employed.